Substituted rhenium trioxides, particularly methylrhenium trioxide (CH.sub.3 ReO.sub.3, MTO) have been used for a variety of organic transformations. For example, MTO has been used for the epoxidation of olefins and their deoxygenation, olefin metathesis and rearrangement of allylic alcohols. (See Herrmann, W.; Fischer, R.; Rauch, M.; Scherer, W. J. Mol. Catal. 86, 243 (1994); Rudolph, J.; Laxma Reddy, K.; Chiang, J.; Sharpless, K. J. Am. Chem. Soc. 119. 6189 (1997),; Zhu, Z.; Espenson, J. J. Mol. Catal. A: Chemical 103, 87 (1995); Hermann, W.; Wagner, W.; Flessner, U.; Volkhardt, U.; Komber, H. Angew. Chem. Int. Ed. Eng. 30, 1636 (1991); and U.S. Pat. No. 5,349,097.) In U.S. Pat. No. 5,349,097, the following reaction is carried out using methylrhenium trioxide on a secondary vinyl carbinol (Example I): ##STR1##
The rearranged product, 2,7-octadien-1-ol, is produced with a selectivity of 100%. This would indicate that a secondary vinyl carbinol rearranges readily to form the corresponding allylic alcohol. No examples are used to teach that dehydration to the diene is an accompanying or alternative reaction. In contrast, the tertiary vinyl alcohols used in the present invention, as described below, yield unexpectedly the diene instead of being rearranged to the corresponding allylic alcohol.
Recently, Zhu and Espenson J. Org. Chem., 61, 324-328 (1996), have reported that MTO catalyzes the formation of symmetrical ethers from primary aliphatic alcohols and unsymmetrical ethers from two different alcohols and the dehydration of alcohols to form olefins; however, the dehydration reaction reportedly required long reaction times and no vinyl carbinols are dehydrated to produce dienes.
The present invention, as described below, shows that certain tertiary vinyl carbinols can be dehydrated conveniently to produce substituted 1,3-butadienes in high yields and with good purity by contacting with substituted rhenium trioxides as catalysts, particularly methyl rhenium trioxide.
This dehydration of tertiary vinyl carbinols to give substituted 1,3-butadienes has traditionally been done by catalysts such as p-toluenesulfonic acid, phosphorous oxychloride in pyridine, molecular sieves, and iodine. (See, Zhu, Z.; Espenson, J., J. Org. Chem. 61, 324-328 (1996); Bartlett, P., et al., J. Am. Chem. Soc. 90, 2049 (1968); Quin. L. D., et al., J. Heterocyclic. Chem. 19, No. 5, 1041-44 (1982), Herz, W. and Juo, R., J. Org. Chem. 50, 618-627 (1985); Markgraf. J. H., et al., Synthetic Communications 14(7), 647-653 (1984); and Paquette, L. A., et al., Tetrahedron Lettters, No. 45, 4033-4036 (1976).) Some of these methods have the disadvantages of requiring long reaction times, producing unwanted by-products or having wastes difficult to dispose of, in contrast to the process of this invention.